Excretory SystemThe kidneys regulate the amount of water, salts and other substances in the blood.

The kidneys are fist-sized, bean shaped structures that remove nitrogenous wastes (urine) and excess salts from the blood.

The ureters are tubes that carry urine from the pelvis of the kidneys to the urinary bladder.

The urinary bladder temporarily stores urine until it is released from the body.

The urethra is the tube that carries urine from the urinary bladder to the outside of the body.

The outer end of the urethra is controlled by a circular muscle called a sphincter.

How blood is Filtered

The filtering units of the kidneys are the nephrons.

There are approximately one million nephrons in each kidney.

The nephrons are located within the cortex and medulla of each kidney.

The tubes of the nephron are surrounded by cells and a network of blood vessels spreads throughout the tissue. Therefore, material that leaves the nephron enters the surrounding cells and returns to the bloodstream by a network of vessels.

Function of the Kidney

The principal function of the kidney is

to filter blood in order to remove

cellular waste products from the body.

2. They regulate the concentrations of

substances found in body fluids

The kidney has other functions but it

is usually associated with the

excretion of cellular waste such as :

1) urea (a nitrogenous waste

produced in the liver from the

breakdown of protein. It is the main

component of urine) ;

Function of Excretory System1. Filtration and excretion of metabolic wastes

2. The regulation of blood content.

3. The regulation of blood pH.

4. Homeostasis.

Function of urinary system

• Excretion• Keeping homeostasis• Keeping acid-base balance• Secretion (rennin,, erytropoetin)

Excreted products:• Product of the metabolism• Water• Hormones• Vitamins• Toxic substances

Kidney function• Step 1: Filtration

• Step 2: Reabsorption

• Step 3: Secretion

• Step 4: Excretion.

Filtration

• During filtration, substances pass from the blood into the Bowman’s capsule.

• Under pressure, water and many small molecules such as salts, urea, glucose and aminoacids pass from glomerulus into Bowman’s capsule.

Reabsorbtion

• The absorbtion of needed materials such as glucose, amino acids and water from nephrons to blood capillaries is called reabsorbtion.

• Water is reabsorbed passively by osmosis. But reabsorbtion of glucose, aminoacids and salt ions occurs by active transport.

• The cells of distal tubule excrete molecules such as penicilin, ammonia, potassium and excess acids. This process is called secretion.

• After secretion, the fluid remaining in the nephrons is called urine.

• Urine contains urea, uric acid, sodium, potassium, calcium, chlorine, phosphorus, water and small amount of cells.

ExcretionExcretion is the removal of metabolic waste from the cells. Metabolic waste is the unwanted material that is formed as a result of the bodies metabolism. That is the large number of chemical reactions that occur in the cells, tissues and organs. The waste products of metabolism are frequently toxic and so must be removed from the body.

Excretory Substances

The metabolic wastes of cells are;

WATER, CO2, NITROGENOUS COMPOUNDS

NITROGENOUS WASTES

•At the end of the catobolisation of aminoacids, AMMONIA(NH3) is formed.

•In some organisms, ammonia is removed frombody directly.

•But in some organisms ammonia is converted to

other substances such as UREA and URIC ACID.

Deamination and Urea SynthesisIn the liver deamination is the process whichbreaks down excess amino acids in to ammoniaand keto acids. Ammonia is still very toxic so itis converted to urea by the process called ureasynthesis. Urea is less toxic than ammonia and socan travel in the blood, but it must be got rid ofquickly because it can still have ill effects. Ureais then transported by the blood from the liver tothe Kidneys where it forms part of urine.

Ammonia reacts with CO2 in the liver to produce

UREA:

2 NH3 + CO2

+ H2O

Catabolism of proteins and nucleic acids results in formation of

so called nonprotein nitrogenous compounds.

Protein

Proteolysis, principally enzymatic

Amino acids

Transamination and oxidative deamination

Ammonia

Enzymatic synthesis in the “urea cycle”

Urea

PARTS OF HUMAN EXCRETORY SYSTEM

1. Kidneys

2. Ureter

3. Urinary bladder

4. Urethra

The urinary

system

Kidney

Ureter

Aorta

Renal vein

Bladder

Renal artery

Vena cava

Urethra

© 2008 Paul Billiet ODWS

The Kidney

Cortex

Medulla

Calyx

Pelvis

Ureter

PapillaPyramid

Column

The nephronBowman’s capsule

Glomerulus

Proximal

convoluted tubule

Capillary

Loop of Henlé

Collecting duct

Distil convoluted

tubule

Branch of renal

vein

Branch of renal

artery

© 2008 Paul Billiet ODWS

Key functions of the nephron

Functions of the Nephron

Filtration

Reabsorption Secretion

Excretion

URINARY BLADDER

Stores urine

URETHRA

Tube that carries urine

from the bladder to the

outside of the body

Reabsorption stage:

water, minerals,

amino acids and

glucose are

reabsorbed by active

transport from the

renal tubule into the

capillaries

Filtration in the glomerulus

Blood enters the glomerulus from a branch of the renal artery

This blood is under high pressure

The capillary walls are one cell thick

The plasma filters though the membrane under pressure

Proteins do not pass Southern Illinois School of Medicine

© 2008 Paul Billiet ODWS

Filtration in the glomerulus

A membrane surrounds

each capillary of the

glomerulus

The blood plasma is

filtered at about 150 litres

per day

Southern Illinois School of Medicine

© 2008 Paul Billiet ODWS

The remaining material is

urine which contains water,

salt and urea

Excretory System Problems

• Kidney stones – crystalized mineral salts and uric acid salts in the urine. Stones block flow of urine and cause excruciating pain.

• Kidney failure - can be caused by long-term diabetes, infections, physical injuries, chemical poisoning. Causes toxic materials to build up to lethal levels.

Dialysis or kidney transplant is the treatment.

Effects of Aging upon Urinary System

• Reduced blood supply to kidneys – less filtering of blood.

• On top of that, the kidney become less efficient with respect to the filtering process.

• Poorer salt-water/pH balance – dehydration more evident in the elderly.

• Bladder control adversely affected.

• In men, the prostate may enlarge and apply pressure to the urethra making urination difficult (surgery required).

Excretory System

UTI (Urinary Tract Infection)

• Is a very common disorder. If the bladder has

become infected, it is known as cystitis. If the

urethra is infected., it is called urethritis.

• Symptoms include painful urination burning

sensation), frequent urination (even if no urine

present) and bloody or brown urine.

• This can lead to chills, fever, nausea, vomiting and

upper abdomen tenderness.

Disorders of the Excretory System

Renal function tests

Detect renal damage

Monitor functional damage

Help determine etiology

glomerular filtration

rate (GFR)

plasma creatinine

plasma urea

urine volume

urine urea

minerals in urine

urine protein

urine glucose

hematuria

osmolality

Laboratory tests of renal function

Biochemical Tests of Renal Function

Measurement of GFR

Clearance tests

Plasma creatinine

Urea, uric acid and β2-microglobulin Renal tubular function tests

Osmolality measurements

Specific proteinurea

Glycouria

Aminoaciduria

Urinalysis

Appearance

Specific gravity and osmolality

pH

osmolality

Glucose

Protein

Urinary sediments

Why Test Renal Function?

To identify renal dysfunction.

To diagnose renal disease.

To monitor disease progress.

To monitor response to treatment.

To assess changes in function that may impact on therapy (e.g. Digoxin, chemotherapy).

When should you assess renal

function?

Older age

Family history of Chronic Kidney disease (CKD)

Decreased renal mass

Low birth weight

Diabetes Mellitus (DM)

Hypertension (HTN)

Autoimmune disease

Systemic infections

Urinary tract infections (UTI)

Nephrolithiasis

Obstruction to the lower urinary tract

Drug toxicity

Studies about Urea Excretion in human

References:

1- Cotran, RS S.; Kumar, Vinay; Fausto, Nelson; Robbins, Stanley L.; Abbas, Abul K. (2005). Robbins and Cotran pathologic basis of disease. St. Louis, MO: Elsevier Saunders. ISBN 0-7216-0187-1.

2- Glodny B, Unterholzner V, Taferner B, et al. (2009). "Normal kidney size and its influencing factors - a 64-slice MDCT study of 1.040 asymptomatic patients". BMC Urology 9: 19. doi:10.1186/1471-2490-9-19. PMC 2813848. PMID 20030823.

3- Bålens ytanatomy (Superficial anatomy of the trunk). Anca Dragomir, Mats Hjortberg and Godfried M. Romans. Section for human anatomy at the Department of medical biology, Uppsala university, Sweden.

4- Walter F. Boron (2004). Medical Physiology: A Cellular And Molecular Approach. Elsevier/Saunders. ISBN 1-4160-2328-3.

5- Clapp, WL. "Renal Anatomy". In: Zhou XJ, Laszik Z, Nadasdy T, D'AgatiVD, Silva FG, eds. Silva's Diagnostic Renal Pathology. New York: Cambridge University Press; 2009.

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